have you looked at leveraging SDM for image customizaion and k3s upgrade controller?

[tim-oe]

I started using SDM to do the initialization of my PIs, creating custom users for ansible and adding keys
https://github.com/gitbls/sdm/tree/master

I've used the k3s upgrade controller for perform the k3s upgrade
https://github.com/rancher/system-upgrade-controller